The statement said the investigation by Washington's Metropolitan Police Department and the US Attorney's Office for the District of Columbia with assistance from the FBI is now closed.

Russian state media reports had quoted Mr Lesin's family as saying he died of a heart attack.

But his mysterious death spawned conspiracy theories that he was murdered, and even preliminary US findings suggested foul play.

Russian officials had criticised a lack of communication from US authorities over Mr Lesin's death.

They said they became aware of details of his injuries only when the medical examiner's report was released.

BBC Russian says Mr Lesin was for a long time considered one of the most influential figures in the Russian media market and in the corridors of power.

He worked as an aide to the presidency between 2004-09, when he helped advise on the creation of the English-language news channel Russia Today.

Mr Putin led tributes to Mr Lesin following news of his death, hailing his "enormous contribution... to the formation of modern Russian media".

Mr Lesin had allegedly amassed millions of dollars in assets in Europe and the US, including $28m in Los Angeles real estate, while working for the Russian government.

Kremlin critics had suggested Mr Lesin was killed by Russian agents because he was about to make a deal with US officials investigating his property holdings in California.

Sergey Vasiliev, a business associate, told the Washington Post that a hotel security guard had checked up on Mr Lesin the night before he was found dead because the guest had not left his room in a long time.

Mr Vasiliev told the newspaper that the guard had found a drunken Mr Lesin on the floor asleep, and he resisted efforts to be helped up.

A cleaner found Mr Lesin the next morning lying in the same spot but non-responsive, added Mr Vasiliev.

The Dupont Circle Hotel, which is not far from the US capital's embassy row area, did not immediately respond to the BBC's request for comment.